The edges will always reconnect to the same core unless it's not available. In 4.0.x, WCCP does not effect CIFS connections (4050 connections), only load balancing the TCP connections outside the 4050 connections. I have manually load balanced edges before via expert mode on the edge GUI, but it's fairly unwieldy. How many edges do you have? I can dig up the procedure if you want to use it.
You can get decent load balancing by setting up both cores so they are both taking edge connections, take the old core offline (stopping the service in the GUI) for several minutes and then bringing it back up. A good number of your edges should now be on the new core and some will still be on the old core.
Also, remember it's best practice to try and keep N+1 at your core. If you loose a core WAE in your cluster and a single Core can't handle the CIFS traffic, you will continue to get CIFS optimization.
Hope that helps,